1. Field of the Invention
The present invention relates to a photolithography process in a semiconductor device manufacturing process, and more particularly to a negative type photoresist composition suitable for a photolithography using a light with a short wavelength such as a light from an ArF excimer laser as an exposure light and a method of forming a pattern using the same.
2. Description of the Related Art
In the manufacturing field of various types of electronic devices among which a representative one is a semiconductor device, there is requirement of a higher density and a higher integration of devices. For this purpose, the fine processing of a half micron order is needed. Therefore, the requirement to photolithography technique for forming a fine pattern becomes increasingly more severe.
One method of forming such a fine pattern is to use a light having a shorter wavelength as an exposure light, when the pattern should be formed using a photoresist. For this purpose, the use of a KrF excimer laser as the exposure light is more positively studied at present for the mass production process of a 256-Mbit DRAM instead of the i line. The manufacture size of the 256-Mbit DRAM is equal to or less than 0.25 .mu.m. The i line which is conventionally used has the wavelength of 365 nm, whereas the KrF excimer laser has the shorter wavelength of 248 nm.
However, a light source with a further shorter wavelength is necessary to manufacture a DRAM having a memory capacity equal to or more than 1 Gbits. The manufacture size of such a DRAM is equal to or less than 0.18 .mu.m. Therefore, a further finer manufacture technique is required. For this reason, the use of an ArF excimer laser having the wavelength of 193 nm to the photolithography process is recently studied to satisfy the requirement. The photolithography using the excimer laser requires increase of cost performance of the laser, because the gas which is the raw materials of the laser oscillation has a short life, and the laser apparatus itself is expensive. Thus, the requirement of high sensitivity is present in addition to the high resolution such that the fine pattern forming process corresponding to the manufacture size can be accomplished.
As such a photoresist composition having high sensitivity, a chemically amplified type photoresist is well known which uses a photo-acid generator which is a sensitizer. In the features of the chemically amplified type photoresist, protonic acid is generated from the photo-acid generator contained in the photoresist through light irradiation of an exposure light. The protonic acid induces acid catalyst reaction to a base resin of the photoresist through heating processing after the exposure. Thus, the remarkably higher sensitivity is accomplished, compared with the conventional photoresist in which the photoreaction efficiency (that is, the reaction per a photon) is less than 1.
As a typical example of the chemically amplified type photoresist, a photoresist composed of a combination of triphenylsulfonium hexafluoloarsenate and poly(p-tert-butoxycarbonyloxy-.alpha.-methylstyrene) which is disclosed in Japanese Laid Open Patent Application (JP-A-Heisei 2-27660) is known as a positive-type photoresist. Also, a photoresist composed of a combination of polyvinylphenol and a melamine derivative is described in Proceeding of SPIE (Vol. 1086, 1989, pp. 34-47) by L. E. Bogan et al. as a negative type photoresist. The chemically amplified type photoresist is widely used as the photoresist for the KrF excimer laser at present for the high resolution and high sensitivity.
The resin which has a benzene ring such as novolak and polyvinylphenol has been used for the photoresist for the g line, the i line, and the KrF excimer laser. However, the resin which contains the benzene ring has very large light absorption of the light having the wavelength equal to or less than 220 nm such as the ArF excimer laser light. For this reason, if these photoresist compositions are used for the ArF excimer laser photolithography, most of the exposure light is absorbed in the photoresist surface. As a result, the laser light does not transmit to the substrate so that it is impossible to form a fine photoresist pattern. Therefore, the photoresist resin which has been used for the g line, the i line, and the KrF excimer laser cannot be applied to the photolithography in which the light with the shorter wavelength equal to or less than 220 nm is used just as it is.
On the other hand, the high etching durability which is necessarily required to the photoresist for a semiconductor manufacturing process is accomplished based on the benzene ring which is contained in the photoresist compositions for the g line, the i line, and the KrF excimer laser. Therefore, the photoresist for the ArF excimer laser needs to be material which has the etching durability without containing any benzene ring, and which has enough transparency to the light with wavelength equal to or less than 220 nm.
A positive type photoresist compositions having enough transparency to the ArF excimer laser with the wavelength of 193 nm and having the dry etching durability are studied for these several years. In the positive type photoresist, the resin containing an alicyclic group is used as base resin. For instance, a copolymer having adamantyl methacrylate unit by Takechi et al., ("Journal of Photopolymer Science and Technology", Vol. 5 (3), 1992, pp. 439-446), a copolymer having isobornyl methacrylate unit by R. D. Allen et al., ("Journal of Photopolymer Science and Technology", Vol. 8 (4), 1995, pp. 623-636, and Vol. 9 (3), 1996, pp. 465-474), and a copolymer having carboxylation tricyclodecyl methyl methacrylate unit by Maeda et al., ("SPIE Proceeding", Vol. 2724, 1996, pp. 377-398) are known.
As described above, the positive type photoresist is known for the photolithography in which the light with the short wavelength equal to or less than 220 nm is used. Such a lithography is represented by the ArF excimer laser photolithography. However, a negative type photoresist is not known. All of the conventional negative type photoresist compositions which are used for the g line, the i line, the KrF excimer laser cannot be applied to the photolithography in which the light with the shorter wavelength, just as it is. This is because a benzene ring is contained in the base resin, so that the light absorption of the light having the short wavelength equal to or less than 220 nm is too large, and most of the exposure light is absorbed in the photoresist surface.